1. Field of the Invention
The present invention relates to a medicament to be used in the fields of medicine, immunology, molecular biology and virology preferentially to prevent and/or treat physical disorders associated with the renin-activated angiotensin system, preferably hypertension and hypertension-associated cardiovascular diseases (CVD).
2. Description of Related Art
The renin angiotensin system (RAS), also known as renin angiotensin aldosteron system (RAAS), is a hormone system that regulates different physiological processes in the body. RAS activity is initiated by the cleavage of the peptide angiotensinogen to the decapeptide angiotensin I (Ang I) by the enzyme renin. The key product of the renin system is the octapeptide hormone angiotensin II (Ang II), which is formed from Ang I by the angiotensin-converting enzyme (ACE). RAS plays a key role in volume regulation and the maintenance of blood pressure. However, excessive activity of the renin system is associated with hypertension and target organ damage.
In recent years it became clear that the renin angiotensin system (RAS) extends well beyond their classical role in blood pressure regulation and salt-water balance. Beside regulating the physiological and pathophysiological processes of cardiovascular and renin tissue, the RAS has been described to act on a number of additional tissues, including, brain, endocrine, sensory, fat and immune cells. Thus the RAS plays an important role in physiological and pathophysiological processes of these tissues as well.
Since physiological and pathophysiological implications of the RAS are extremely broad medications targeting the RAS have become key clinical tools in the treatment of cardiovascular and renal diseases, such as hypertension, heart failure and diabetic nephropthy. Moreover different studies show that blocking the RAS does not only influence cardiovascular diseases connected to high blood pressure but can also reduce cardiovascular events linked to inflammatory processes such as atherosclerosis. These basic research and animal studies strongly support angiotensin II as a proinflammatory mediator, which directly induces atherosclerotic plaque development and heart remodeling.
In addition, RAS seems to be central not only to the inflammatory aspects of atherosclerosis but also of autoimmune diseases such as multiple sclerosis.
Furthermore, evidence suggests that blockade of the renin-angiotensin system decreases the occurrence of new-onset diabetes and reduces the risk of diabetic complications. Other studies provide an overview of the effects of Ang II leading to the development of insulin resistance and its implications for diabetes. Components of the renin-angiotensin system have a complex interaction with insulin action and the development and progression of metabolic diseases.
RAS, Inflammatory Disorders and Autoimmune Disorders (Atherosclerosis and Multiple Sclerosis)
Atherosclerosis is a chronic inflammatory disease, which involves vascular cells, immune system, and several organs. Although leukocytes, endothelial and smooth muscle cells have been shown to play a crucial role in atherosclerotic inflammation, recent evidence also supports a direct activity for cytokines and chemokines, factors that have been shown to modulate inflammatory processes. Recent studies now suggest new inflammatory activities for the peptide hormone angiotensin II. The renin-angiotensin system serves an important role in promoting inflammation, since angiotensin II induces proatherosclerotic cytokine secretion and increases endothelial dysfunction. Angiotensin II regulates not only cytokine, chemokine, and growth factor secretion within the arterial wall but regulates also the expression of adhesion molecules (VCAM-1, ICAM-1, P-selectin). Beside this it has been shown that the renin-angiotensin system can modulate the activation of complement system in both atherosclerosis and renal injury. This inflammatory cascade activates the vascular inflammatory response by increasing inflammatory cell recruitment to intima. Recruited cells can produce angiotensin II, resulting in a positive feedback response, which can maintain this inflammatory vicious circle.
Recently different publications show that the intersection between chronic inflammatory diseases like multiple sclerosis (MS) and the most common of all of the human chronic diseases, atherosclerosis, may go far beyond the root “sclerosis”, which is shared in both their names. They showed that the RAS also plays a major role in autoimmunity, exemplified by multiple sclerosis (MS) and its animal model, experimental autoimmune encephalomyelitis (EAE). Using proteomics, the authors observed that RAS is up-regulated in brain lesions of MS. Blocking angiotensin II production with ACE inhibitors or inhibiting angiotensin II signaling with angiotensin II receptor blockers suppressed autoreactive TH1 and TH17 cells and promoted antigen-specific CD4_FoxP3_regulatory T cells (Treg cells). Treatment with ACE inhibitors induces abundant CD4_FoxP3_T cells with sufficient potency to reverse paralytic EAE. Therefore, authors concluded that modulation of the RAS is an attractive therapeutic strategy for application to human autoimmune diseases.
RAS and Cardiovascular Diseases—Hypertension
Cardiovascular disease (CVD) is the leading cause of death throughout the world. According to the World Health Organization (WHO) approximately 30% of all global deaths can be attributed to CVD. CVD is caused by disorders of the heart and blood vessels and encompasses various manifestations. These include myocardial infarction, stroke, heart failure, and end stage renal disease. The most prevalent risk factor for CVD is hypertension. More than a quarter of the world's adult population had hypertension in 2000 and if appropriate action is not taken, this numbers will increase continuously.
Hypertension, commonly referred to as high blood pressure is defined as chronically elevated blood pressure with a systolic blood pressure above 140 mmHg and/or a diastolic blood pressure above 90 mmHg. Guidelines defined by the “Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure” suggest that persons with a blood pressure between 120 and 139 mmHg systolic and/or a blood pressure between 80 and 89 mmHg diastolic should be considered pre-hypertensive and require health-promoting changes to prevent CVD. Therefore, lowering the blood pressure is an important strategy to prevent CVD. As first step, blood pressure reduction can be achieved by changes in life style targeting the primary factors like unhealthy diet, physical inactivity, and smoking. However, treatment of essential hypertension requires specific therapies. A key regulator of the blood pressure is the renin-angiotensin system (RAS) which has become an attractive target for therapeutic intervention. Therefore pharmaceuticals that specifically act on components of the RAS have become important clinical tools in the treatment of hypertension.
The RAS pathway is a cascade beginning with the cleavage of angiotensinogen by renin. Renin is an aspartyl protease synthesized and stored primarily in the granules of juxtaglomerular cells in the kidney and has high substrate specificity for angiotensinogen. Angiotensinogen is mainly formed and constitutively secreted into the circulation by hepatic cells. It is cleaved at the N-terminus by renin to form the decapeptide Angiotensin I (Ang I; the 1-10 peptide) which is rapidly converted into the biological active octapeptide angiotensin II (Ang II; the 1-8 peptide). In contrast to Ang II, Ang I appears to have no biological activity and exists solely as a precursor for Ang II. Cleavage of Ang I is mediated basically, but not exclusively by the angiotensin-converting enzyme (ACE). This membrane-bound metalloproteinase is expressed on the surface of endothelial cells with the highest concentrations found on the vascular epithelium in the lung. Besides ACE chymase has been shown to produce Ang II. Ang II can also directly be generated from angiotensinogen by enzymes like tonin and cathepsin. In addition, other Ang I- and Ang II-derived, functional peptides can be found in the circulation. These are generated by amino-, carboxy- or endopeptidases and include Ang(1-9), Ang(1-7), Ang III (the 2-8 peptide) and Ang IV (the 3-8 peptide). A carboxypeptidase, known as angiotensin-converting enzyme II (ACE2), acts on Ang I as well as Ang II. ACE2 generates Ang1-9 from Ang I and Ang1-7 from Ang II. Ang1-9 can then be further converted to Ang1-7 by ACE. In contrast to Ang II, which elevates blood pressure and appears to be the major mediator of vascular remodeling in hypertension, Ang1-7 peptide promotes vasodilation and by that may counteract the potentially detrimental actions of Ang II. The peptide Ang1-7 acts via its receptor the mas oncogen product (MAS).
Ang II and Ang 1-7 are considered as the main effector peptides of the RAS, while Ang III and Ang IV have some lesser activity (approximately 40% of the activity of Ang II). The actions of Ang II are mediated predominantly by two seven transmembrane receptors termed Ang II receptors, type 1 (AT1; subtypes 1a and 1b) and type 2 (AT2). The AT1 and AT2 subtypes bind Ang II similarly, but have a different cellular localization and are differentially expressed in diverse tissues. Most of the Ang II hypertensinogenic actions are attributed to the AT1 receptor.
Throughout the body Ang II is a potent vasoconstrictor. In the kidneys it constricts glomerular arterioles thereby increasing systemic arterial blood pressure and decreasing blood flow. In the adrenal cortex, it causes the release of aldosterone which in turn causes the tubules in the kidneys to reabsorb more sodium and water from the urine. It also acts on the central nervous system to increase a person's appetite for salt and to make them feel thirsty. Additionally, Ang II stimulates the release of Anti Diuretic Hormone (ADH).
The classical role of components of the RAS is to act as endocrine factors in order to maintain blood pressure and electrolyte as well as fluid balance. In addition to this circulating RAS a local angiotensin-generating cascade exists in several tissues. The so-called tissue RAS can act locally as a paracrine and/or autocrine factor and can operate, in whole or in part, independently of the circulating counterpart.
Currently several drugs are on the market to treat hypertension. These encompass for example diuretics and calcium-channel blockers and include numerous pharmaceuticals that specifically target components of the RAS. The latter include ACE inhibitors which act by binding to the active side of ACE and interfering with the ability of the enzyme to bind and cleave its substrates. Characteristic side effects of ACE inhibitors are dry cough and first dose hypotension/angioneurotic oedema. Another class of pharmaceuticals that target the RAS is angiotensin receptor (AT1) blockers (ARBs). ARBs specifically interfere with the function of Ang II by blocking the binding of angiotensin II to the AT1 receptor. Recently, a new compound targeting the RAS, namely Aliskerin a drug which inhibits renin has been released on the market.
In the art it is also suggested to use antagonists for Ang II which show a higher binding affinity to AT1 receptor than Ang II. In document WO 2005/044313 A compounds are disclosed which can be used in the treatment of heart diseases, diseases associated with fibrosis and atherosclerosis. The compounds disclosed in WO 2005/044313 A comprise an octapeptide having the general formula X1X2VYIHPX3 whereby X1 may be any amino acid residue, X2 arginine or N-alkylated arginine or a mimetic of arginine, and X3 may be an amino acid residue containing a hydrophobic side chain. These compounds have a higher binding affinity to the AT1 receptor than angiotensin II (antagonistic activity).
In GB 2001653 A a compound being derived from angiotensin II and having the general formula XRVYIHPY is disclosed, wherein X represents an α-aminooxy aliphatic acyl group and Y may be leucin, isoleuin, alanin or threonin. Such a compound can be used in the treatment of renal hypertension.
WO 2002/087504 A, WO 2001/043761 A, WO 2001/098325 A and WO 2000/002905 A provide compounds which function as angiotensin II analogues.
Although different drugs to treat hypertension are available on the market, hypertension still remains inadequately handled. Poor overall treatment success lies on the one hand in the asymptomatic nature of hypertension and on the other side in the necessity for long-term treatment with medications that requires at least once daily self-administration.
Recently, active immunotherapy has become of increasing interest as a potential new strategy to treat hypertension and associated disorders.
The practicability of vaccination against components of the RAS to treat hypertension has been shown in different animal models (Michel-J B et al., Am Heart J. 1989; 117:756). In one of the first approaches it has been shown that vaccination against renin was effective in lowering blood pressure. However, this approach has not been pursued in following years since animals started to suffer from autoimmune nephritis (Michel-J B et al., Circulation. 1990; 81(6):1899-910). Other approaches aimed at inducing an immune response against components of the RAS that are expressed as transmembrane proteins on the cell surface, such as ACE and AT1R. Several research groups have investigated active immunization against AT1R. Although some studies report that antibodies against the N-terminus of the AT1R can attenuate the development of hypertension in spontaneously hypertensive rats, most approaches had no significant effect on blood pressure. Data on active immunization against ACE is very limited. One report describes the vaccination of rabbits but only 1 out of 50 animals made detectable anti ACE antibodies (Soffer-R L et al., Fed. Proc. 1983; 42(19):2735-9). No reports are available on active immunization against angiotensinogen, however several studies explored the feasibility of vaccination against angiotensin I and angiotensin II.
Vaccination with Ang I conjugated to carrier proteins (e.g. keyhole limpet haemocyanin (KLH)) led to the induction of high antigen-specific humoral immune responses. In experimental settings using different animal models the vaccination-induced antibodies against angiotensin I appeared to be functional, since (i) they were able to bind angiotensin I as revealed by Western blot analysis and (ii) the blood pressure was significantly reduced, indicating that the effects of angiotensin on the RAS were blocked (Downham et al., Br J Clin Pharmacol. 2003; 56:505-12.). By contrast, in human healthy volunteers the blood pressure lowering effect was not seen (Downham et al., 2003). This finding was further confirmed in a study with hypertensive patients who were treated with a 12 amino acid analogue of Ang I covalently linked to KLH and adsorbed to Alum (referred to as PMD3117) (Brown et al., Clin Sci. 2004; 107:167-73). Importantly, this treatment regimen was well tolerated and induced a long lasting, antigen-specific humoral immune response. Additionally, this treatment showed an effect on the renin system as detected by changes in renin and aldosterone levels. However, vaccination with PMD3117 showed no influence on the blood pressure as compared to the placebo control group (Brown et al., 2004). In contrast, a slightly different further development of this Ang I vaccine which was developed by Protherics and replaced Alum by a new adjuvant, namely Co Vaccine HT™ did show an effect. Administration of this new vaccine formulation resulted in a 10-fold increase in anti-angiotensin antibody titers in a preclinical setting and human healthy subjects showed changes in systolic and diastolic blood pressure. However, blood pressure was only slightly reduced and this only during rest periods but not during phases of activity which would be of more importance.
Other approaches to induce antibodies that are able to block the RAS used angiotensin II-derived peptides as antigens. In contrast to a previous study where injection of Ang II-carrier protein conjugates did not result in lowering blood pressure, vaccination with Ang II coupled to virus-like particles (VLP) led to the induction of a high anti-angiotensin specific humoral immune response, that was paralleled with a statistically significant reduction of blood pressure (Ambühl et al., J. Hypertension. 2007; 25:63-72.). In a recent clinical study however, this blood pressure lowering effect could not be monitored upon vaccination using angiotensin II coupled to virus like particles, indicating that the induced humoral immune response induced by this peptide vaccine might not be optimal or sufficient. Therefore, there remains a need in the art to provide new and more effective vaccines targeting angiotensin peptides.